German Utility Model 77 15 006 discloses a toothbrush having a slotted or perforated plate, through the slots or perforations of which bristle clusters protrude upward. The slotted or perforated plate is provided with a manually actuated adjusting device that makes it possible to vary the distance between the slotted or perforated plate and the surface, from which the bristle clusters protrude, namely in such a way that the free length of the bristle clusters can be respectively extended or shortened. This makes it possible to respectively decrease or increase the hardness of the toothbrush. One less advantageous aspect of this arrangement can be seen in that—leaving aside the already costly construction—only the freely protruding length of all bristle clusters arranged on the brush head is varied with a single adjustable slotted or perforated plate, respectively.
U.S. Pat. No. 2,274,042 discloses a manually operated toothbrush, in which bristle clusters of identical dimensions protrude from the toothbrush head, namely from surfaces thereof that are arranged at different heights. The quality as well as the length and the thickness of all bristle clusters are identical such that the flexural strength of all bristle clusters is also identical. Although the brushing ends of a few bristle clusters protrude from the brushing plane such that they respectively lie above or below the brushing ends of other bristle clusters, all bristle clusters have the same flexural strength because they protrude by the same length.
A manually operated toothbrush is also known from U.S. Pat. No. 6,553,604, wherein bristle clusters of different cross sections protrude from a surface of the brush head of this toothbrush. In this case, bristle clusters situated on the edge are arranged in openings that are larger than the cross section of the individual bristle clusters such that they are flexible in the longitudinal direction of the manually operated toothbrush. This enables these bristle clusters to better penetrate into the interdental spaces when the toothbrush is moved back and forth while brushing the teeth. The bristle clusters are supported in the recesses by means of barrel-shaped thickenings arranged on their ends. Although a toothbrush of this type functions well, its manufacture and assembly are more costly than those of conventional toothbrushes.